[Show abstract][Hide abstract] ABSTRACT: This paper focuses on the investigation of nanooxide composites SiO2/TiO2/X (X = SnO2, NiO)
synthesized by controlled low�temperature hydrolysis of TiCl4, SnCl4 (followed by thermal treatment of some
samples) on nanosilica surface (specific surface area 300 m2/g) and by thermolysis of Ni(NO3)2 ⋅ 6H2O at
600°C. The effect of the nature and concentration of a doping agent on the phase composition of the com�
posites and their physicochemical properties is determined. The properties of the synthesized systems are
examined by means of XRD analysis, nitrogen adsorption, potentiometric titration, and photon correlation
Protection of metals and physical chemistry of surfaces 09/2013; 49(49):541-547. DOI:10.1134/S2070205113050067 · 0.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Morphological characteristics of CuO- and NiO-doped silica/titania nanocomposites are analyzed using atomic force microscopy and low-temperature nitrogen adsorption. The different types of pores (nano-, meso- and macropores) in the powder composites are modeled as voids between spherical nanoparticles packed in random aggregates. It is shown that specific surface area, total pore volume, average pore radius, incremental pore size distribution and changes in relationships between these characteristics of the composites reveal a non-linear behavior depended on the presence of the dopants. The textural and atomic force microscopy investigations suggest that processes of aggregation differ from each other depending on the type of doping oxide. Fractal dimension, estimated according to Frenkel-Halsey-Hill equation using the adsorption branch, has values about 2.50–2.60 and indicates the aggregate formation.
[Show abstract][Hide abstract] ABSTRACT: SiO2/TiO2/CuO composites have been synthesized by deposition technique using low temperature hydrolysis of TiCl4 and thermolysis of Cu(CH3CO2)2 · H2O at silica A-300 surface. The properties of the samples have been explored by means of XRD, nitrogen adsorption, potentiometric titration, and photon correlation spectroscopy. As the results indicate, there are both anatase and some amount of rutile formed at CCuO = 1 wt. %. A gradual shift of the point of zero charge (from pH = 3.48 to 6.60) has been observed with increasing CuO content.
[Show abstract][Hide abstract] ABSTRACT: Adsorption of low-molecular adsorbates (nonpolar hexane, nitrogen, weakly polar acetonitrile, and polar diethylamine, triethylamine, and water) onto individual (silica, alumina, titania), binary (silica/alumina (SA), silica/titania (ST)), and ternary (alumina/silica/titania, AST) fumed oxides was studied to analyse the effects of morphology and surface composition of the materials. Certain aspects of the interfacial phenomena dependent on the structural characteristics of oxides were analysed using calorimetry, (1)H NMR, and Raman spectroscopies, XRD, and ab initio quantum-chemical calculations. The specific surface area S(BET,X)-to-S(BET,N(2)) ratio (X is an organic adsorbate) changes from 0.68 for hexane adsorbed onto amorphous SA8 (degassed at 200 degrees C) to 1.85 for acetonitrile adsorbed onto crystalline alumina (degassed at 900 degrees C). These changes are relatively large because of variations in orientation, lateral interactions, and adsorption compressing of molecules adsorbed onto oxide surfaces. Larger S(BET,X)/S(BET,N(2)) values are observed for mixed oxides with higher crystallinity of titania or/and alumina phases in larger primary nanoparticles with greater surface roughness and hydrophilicity. Polar adsorbates can change the structure of aggregates of oxide nanoparticles that can, in turn, affect the results of adsorption measurements.
Journal of Colloid and Interface Science 08/2010; 348(2):546-58. DOI:10.1016/j.jcis.2010.04.062 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Textural and adsorptive characteristics, surface structures, and the volume of individual, binary and ternary nanooxide particles
with SiO2, Al2O3 and TiO2 were investigated. These materials’ interactions with low and high molecular weight compounds were investigated using adsorption,
NMR, TSDC, DRS, FTIR, TPD–MS, Auger spectroscopy, optical spectroscopy, DLS, titration and microcalorimetry. The presence
of a structural hierarchy of particles from primary (10–50nm), their aggregates (50–1000nm) and agglomerates of aggregates
(> 1μm) to visible flocculi affects textural features of the oxides, adsorption of different compounds and the behaviour
of materials in liquid media.
[Show abstract][Hide abstract] ABSTRACT: Morphological, structural, and adsorptive characteristics of such fumed oxides as alumina, silica, composite silica/alumina and alumina/silica/titania were studied using a variety of experimental methods. Heating of nanooxides caused several processes resulting in the temperature dependent structural changes of the materials because of changes in the amounts of intact and dissociatively adsorbed water not only at the surface of the nanoparticles but also in their volume that lead to changes in the oxide matrix structure. These processes dependent on the composition of nanooxides are much stronger for nanosilica than for alumina or composite oxides. The morphology of primary nanoparticles is more stable on different treatments than the structure of secondary and ternary particles. The amounts of water adsorbed onto the nanooxides from air correspond to the amounts of water strongly bound (unfrozen at T < 273 K) to the oxide surfaces in aqueous suspensions.Graphical abstractHeating history can strongly affect many physicochemical properties of nanooxides, because of changes in the amounts of intact and dissociatively adsorbed water at the surface of nanoparticles and in their volume.
[Show abstract][Hide abstract] ABSTRACT: Comparative study of water confined in highly disperse and porous adsorbents and bioobjects by 1H NMR spectroscopy and thermally stimulated depolarisation current (TSDC) methods at T < 273 K revealed the presence of several dynamic processes linked to the mobility of (i) polar bonds responsible for dipolar relaxations (TSDC) at 90 < T < 200–220 K when the molecular mobility (diffusion) is absent; (ii) water molecules responsible for the 1H NMR spectra at T > 200 K; (iii) protons and ions resulting in direct current (dc) relaxation (TSDC) at T > 210–220 K. According to the 1H NMR spectra recorded on layer-by-layer freezing-out of bulk and interfacial waters bound in solid adsorbents and bioobjects, there are four types of confined water attributed to strongly (ΔG < − 1 kJ/mol) and weakly (ΔG > − 1 kJ/mol) bound and strongly (δH = 4–5 ppm) and weakly (δH = 1–2 ppm) associated waters. Several factors such as structural, textural and morphological characteristics of adsorbents and bioobjects, partial hydrophilic/hydrophobic surface functionalisation of adsorbents, amounts of water and other co-adsorbates (organic solvents, ions, etc.) affect contributions of the mentioned types of bound water.
Colloids and Surfaces A Physicochemical and Engineering Aspects 03/2009; 336(1-3-336):147-158. DOI:10.1016/j.colsurfa.2008.11.043 · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Co-adsorption of water and methane onto polymeric adsorbent LiChrolut EN, activated carbon adsorbent, fumed alumina and Silochrome modified by 3-aminopropylmethyldimethoxy silane was studied using 1H NMR spectroscopy with layer-by-layer freezing out of bulk and bound adsorbates. At a certain amount of adsorbed water the adsorption of methane can increase. Bound water can be in strongly (changes in Gibbs free energy ΔG−1kJ/mol) bound and strongly (chemical shift of the proton resonance δH=3–6ppm) and weakly (δH=1–2ppm) associated states. With the presence of adsorbed methane contribution of weakly associated water increases.
[Show abstract][Hide abstract] ABSTRACT: Morphological, structural, adsorption, and catalytic properties of highly disperse titania prepared using sulfate and pyrogenic methods, and fumed titania-containing mixed oxides, were studied using XRD, TG/DTA, nitrogen adsorption, (1)H NMR, FTIR, microcalorimetry on immersion of oxides in water and decane, thermally stimulated depolarization current (TSDC) and catalytic photodecomposition of methylene blue (MB). Phase composition and aggregation characteristics of nanoparticles (pore size distribution) of sulfate and pyrogenically prepared titania are very different; temperature dependent structural properties are thus very different. Catalytic activity for the photodecomposition of MB is greatest (per gram of TiO(2) for the pure oxide materials) for non-treated ultrafine titania PC-500, which has the largest S(BET) value and smallest particle size of the materials studied. However, this activity calculated per m(2) is higher for PC-105, possessing a much smaller S(BET) value than PC-500. The activity per unit surface area of titania is greatest for the fumed silica-titania mixed oxide ST20. Calcination of PC-500 at 650 degrees C leads to enhancement of anatase content and catalytic activity, but heating at 800 and 900 degrees C lowers the anatase content (since rutile appears) and diminishes catalytic activity, as well as the specific surface area because of nanoparticle sintering.
Journal of Colloid and Interface Science 12/2008; 330(1):125-37. DOI:10.1016/j.jcis.2008.10.049 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Morphological and structural characteristics of a variety of powder nanocomposites with fumed oxides (silica, silica/alumina, silica/titania) and different linear polar polymers (poly(ethylene oxide), poly(ethylene glycol), poly(vinyl alcohol), poly(vinyl pyrrolidone), polydimethylsiloxane and proteins (ossein, gelatine, BSA)), were analyzed using nitrogen adsorption, infrared (IR) spectroscopy, AFM, and TPD MS methods. A monolayer or lower coverage of oxide nanoparticles by linear polar polymers results in relatively small changes in the specific surface area and adsorption capacity compared with similarly treated fumed oxides alone. The pore size distributions of dried solid residual oxide/polymer samples demonstrate a more ordered pore structure than the initial powders. This structure, as well as the morphology of secondary particles, depends slightly on the content of polymers (Cpol) at coverage less than a monolayer. If polymer–polymer interactions are weaker than polymer–oxide interactions, the perturbation degree Ф (normalized to molecular weight of a polymer segment mseg) of surface silanols at fumed silica A-300 depends very weakly on the type of adsorbed polymers. Among the studied polymers only PVA demonstrates Ф(Cpol/mseg) values smaller than the other systems because of the formation of strong hydrogen bonds between PVA molecules.
[Show abstract][Hide abstract] ABSTRACT: The structural and adsorption characteristics of polymer adsorbent LiChrolut EN and the behavior of adsorbed water and water/organic mixtures were studied using adsorption, microcalorimetry, transmission and scanning electron microscopy, mass spectrometry, infrared spectroscopy, 1H NMR spectroscopy with layer-by-layer freezing-out of liquids (190-273 K), and thermally stimulated depolarization current method (90-265 K). This adsorbent is characterized by large specific surface area (approximately 1500 m2/g) and pore volume (0.83 cm3/g) with a major contribution of narrow pores (R<10 nm) of a complicated shape (long hysteresis loop is in nitrogen adsorption-desorption isotherm). The adsorbent includes aromatic and aliphatic structures and oxygen-containing functionalities and can effectively adsorb organics and water/organic mixtures. On co-adsorption of water and organics (dimethyl sulfoxide, chloroform, methane), there is a weak influence of one on another adsorbate due to their poor mixing in pores. Weakly polar chloroform displaces a fraction of water from narrow pores. These effects can explain high efficiency of the adsorbent in solid-phase extraction of organics from aqueous solutions. The influence of structural features of several carbon and polymer adsorbents on adsorbed nitrogen, water and water/organics is compared on the basis of the adsorption and 1H NMR data.
Journal of Colloid and Interface Science 08/2008; 323(1):6-17. DOI:10.1016/j.jcis.2008.04.005 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Hydrated powders of non-gelatinised starch and hydrogels of gelatinised starch alone or with addition of modified nanosilica (with grafted aminopropylmethylsilyl groups substituting one-third of surface silanols) were studied using broadband dielectric relaxation spectroscopy (DRS), thermally stimulated depolarisation current (TSDC) method and 1H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial waters. The 1H NMR and TSDC techniques with the use of Gibbs–Thomson relation for the freezing point depression allow us to calculate: (i) the thermodynamic parameters of interfacial water weakly and strongly bound to polymer molecules and nanoparticles; (ii) size distributions of pores filled by structured water; (iii) surface area and volume of micro-, meso- and macropores. The DRS and TSDC results for hydrogels and hydrated powders with starch/modified fumed silica show that the β- and γ-relaxations of starch are strongly affected by water and functionalised silica nanoparticles which slow down both low- and high-frequency and low- and high-temperature relaxations.
Colloids and Surfaces A Physicochemical and Engineering Aspects 05/2008; 320(1-3-320):247-259. DOI:10.1016/j.colsurfa.2008.02.004 · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A variety of fumed oxides such as silica, alumina, titania, silica/alumina (SA), silica/titania (ST), and alumina/silica/titania (AST) were characterized. These oxides have different specific surface areas and different primary particle composition in the bulk and at the surface. These materials were studied by FTIR, NMR, Auger electron spectroscopy, one-pass temperature-programmed desorption with mass spectrometry control (OP TPDMS), microcalorimetry, and nitrogen adsorption. Nonlinear changes in the surface content of alumina in SA and AST and titania in ST and AST samples with increasing oxide content along with simultaneous changes in their specific surface area cause complex dependencies of the heat of immersion in water and desorption of water on heating on the structural parameters. Simultaneous analysis of changes in the surface phase composition, in the concentration of hydroxyls, and in the structural characteristics reveals that at a low content of the second phase the structural characteristics (e.g., S(BET)) are predominant; however, at a large content of these oxides the phase composition plays a more important role.
Journal of Colloid and Interface Science 11/2007; 314(1):119-30. DOI:10.1016/j.jcis.2007.05.025 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Interaction of poly(vinyl alcohol) (PVA) with fumed silica was investigated in the gas phase and aqueous media using adsorption, broadband dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization current (TSDC), infrared spectroscopy, thermal analysis, and one-pass temperature-programmed desorption (OPTPD) mass-spectrometry (MS) methods. PVA monolayer formation leads to certain textural changes in the system (after suspension and drying) because of strong hydrogen bonding of the polymer molecules to silica nanoparticles preventing strong interaction between silica particles themselves. This strong interaction promotes associative desorption of water molecules at lower temperatures than in the case of silica alone. Interaction of PVA with silica and residual water leads to depression of glass transition temperature (T(g)). There are three types of dipolar relaxations at temperatures lower and higher than the T(g) value. A small amount of adsorbed water leads to significant conductivity with elevating temperature.
Journal of Colloid and Interface Science 09/2007; 312(2):201-13. DOI:10.1016/j.jcis.2007.03.065 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Polymethylsiloxane (PMS) hydrogel (C(PMS)=10 wt%, soft paste-like hydrogel), diluted aqueous suspensions, and dried/wetted xerogel (powder) were studied in comparison with suspensions and dry powders of unmodified and silylated nanosilicas and silica gels using (1)H NMR, thermally stimulated depolarization current (TSDC), quasielastic light scattering (QELS), rheometry, and adsorption methods. Nanosized primary PMS particles, which are softer and less dense than silica ones because of the presence of CH(3) groups attached to each Si atom and residual silanols, form soft secondary particles (soft paste-like hydrogel) that can be completely decomposed to nanoparticles with sizes smaller than 10 nm on sonication of the aqueous suspensions. Despite the soft character of the secondary particles, the aqueous suspensions of PMS are characterized by a higher viscosity (at concentration C(PMS)=3-5 wt%) than the suspension of fumed silica at a higher concentration. Three types of structured water are observed in dry PMS xerogel (adsorbed water of 3 wt%). These structures, characterized by the chemical shift of the proton resonance at delta(H) approximately 1.7,3.7, and 5 ppm, correspond to weakly associated but strongly bound water and to strongly associated but weakly or strongly bound waters, respectively. NMR cryoporometry and QELS results suggest that PMS is a mesoporous-macroporous material with the textural porosity caused by voids between primary particles forming aggregates and agglomerates of aggregates. PMS is characterized by a much smaller adsorption capacity with respect to proteins (gelatin, ovalbumin) than unmodified fumed silica A-300.
Journal of Colloid and Interface Science 05/2007; 308(1):142-56. DOI:10.1016/j.jcis.2006.12.053 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Applications of thermally stimulated depolarisation current (TSDC) technique to a variety of systems with different dispersion phases such as disperse and porous metal oxides, polymers, liquid crystals, amorphous and crystalline solids, composites, solid solutions, biomacromolecules, cells, tissues, etc. in gaseous or liquid dispersion media are analysed. The effects of dipolar, direct current (dc) and space charge relaxations are linked to the temperature dependent mobility of molecules, their fragments, protons, anions, and electrons and depend on thermal treatment, temperature and field intensity of polarisation, heating rate on depolarisation or cooling rate on polarisation. Features of the relaxation mechanisms are affected not only by the mentioned factors but also by morphological, structural and chemical characteristics of materials. The interfacial phenomena, especially the role of interfacial water, received significant attention on analysis of the TSDC data. Comparison of the data of TSDC and dielectric relaxation spectroscopy (DRS), differential scanning calorimetry (DSC), 1H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial water, adsorption/desorption of nitrogen, water and dissolved organics demonstrates high sensitivity and information content of the TSDC technique, allowing a deeper understanding of interfacial phenomena.
Advances in Colloid and Interface Science 03/2007; 131(1-2):1-89. DOI:10.1016/j.cis.2006.11.001 · 7.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fumed oxides SiO2/Al2O3 (SA), SiO2/TiO2 (ST) and Al2O3/SiO2/TiO2 (AST) at different content of alumina and titania were investigated by one-pass temperature-programmed desorption (OPTPD) time-of-flight mass-spectrometry (TOFMS), Auger electron spectroscopy (AES), NMR, FTIR, thermally stimulated depolarization current (TSDC), microcalorimetry, adsorption of nitrogen, water, (dimethylamino)azobenzene (DMAAB) and metal ions (Pb(II) and Ni(II)). It was shown that all the studied adsorption/desorption and energetic properties of mixed fumed oxides depend strongly on the surface content of alumina (shown as a surface content of aluminum, ) in SA and AST and titania (shown as a surface content of titanium, ) in ST and AST. Many of these properties demonstrate clear correlations with the and values over the total range of alumina and titania content in the materials.
[Show abstract][Hide abstract] ABSTRACT: A new technique of calculation of a distribution function of activation energy (f(E)) of shear viscosity based on a regularization procedure applied to the Fredholm integral equation of the first kind has been developed using the Baxter-Drayton and Brady model for concentrated and flocculated suspensions. This technique has been applied to the rheological data obtained at different shear rates for aqueous suspensions with fumed silica A-300 and low-molecular (3,4,5-trihydroxybenzoic acid and 1,5-dioxynaphthalene) or high-molecular (poly(vinyl pyrrolidone) of 12.7 kDa and ossein of 20-29 kDa) compounds over a wide concentration range (up to 25 wt% of both components) and at different temperatures. Monomodal f(E) distributions are observed for the suspensions with individual A-300 or A-300 with a low amount of adsorbed organics. In the case of larger amounts of nanosilica and organics the f(E) distributions are multimodal because of stronger structurization and coagulation of the systems that require a high energy to break the coagulation structures resisting to the shear flow.
Journal of Colloid and Interface Science 01/2007; 304(1):239-45. DOI:10.1016/j.jcis.2006.08.029 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Successive interaction of different pairs of water-soluble polymers (poly(ethylene glycol) (PEG), poly(vinyl pyrrolidone) (PVP), poly(vinyl alcohol) (PVA)), proteins (bovine serum albumin (BSA), ovalbumin, gelatin, and ossein), and smaller organics such as lecithin (1-stearoyl-2-oleoyl phosphatidylcholine, SOPC) and Aethonium (1,2-ethylene-bis(N-dimethyl carbodecyl oxymethyl) ammonium dichloride) with nanosilicas A-300 (S(BET)=232 and 297 m(2) g(-1)) and A-50 (S(BET)=52 m(2)g(-1)) was studied using dynamic light scattering, adsorption, and infrared (FTIR) spectroscopy methods. Time-dependent rearrangement of particle size distributions (PSDs) depicts appearance of both smaller and larger aggregates for silica/PEG(I-first adsorbate)/BSA(II-second adsorbate) and silica/PVP(I)/BSA(II) (i.e., BSA adsorbs onto PEG/silica or PVP/silica) than that for silica/organic compound I. However, in the cases of PVA(I)-BSA(II) and PVA(I)-SOPC(II) a similar effect is not observed because only increased aggregation occurs. The successive equilibrium adsorption of similar pairs shows a diminution of the adsorption of the second compound (gelatin, ovalbumin) with increasing amount of the first adsorbed polymer (PEG or PVP).
Journal of Colloid and Interface Science 09/2006; 300(1):20-32. DOI:10.1016/j.jcis.2006.03.034 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Different surface sites of silica, alumina, titania, and related mixed oxides, and pre-adsorbed poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG), affect the interaction with Ni(II), Cd(II), and Pb(II) studied using adsorption and potentiometric titration methods. Bridging hydroxyls (Brönsted acid sites) capable of taking part in ion-exchange reactions, and pre-adsorbed polymers, enhance the adsorption of metal ions at pH < 7. At pH > 7 PVA adsorbed on silica slightly enhances the adsorption of metal ions but pre- adsorbed PEG gives the opposite result. PEG has only electron-donor functionalities (C-O-C) which reduce the number of possible adsorption sites. PVA has COH groups with both electron-donor and proton-donor properties, which can effectively interact with metal ions and their hydroxy species.